It has become common practice to protect various forms of identification cards and other documents, including driver's licenses, student identification cards, security system identification documents, and the like, by sealing such documents into covers formed of thin, tough, transparent plastic film. The best known protective film for this purpose is a laminate that includes an outer film of hard, tough, abrasion-resistant biaxially oriented thermoset polyester resin coated with an inner layer of a thermoplastic adhesive resin activatable by heat and pressure. The polyester resin for the base film is usually polyethylene terephthalate; the most frequently used thermoplastic adhesive resin is polyethylene. To complete a protective cover on an identification card or like document, the document is usually placed between two sheets of the laminating film and then passed through a laminating press in which heat and pressure are applied to activate the thermoplastic adhesive, bonding the film to the surfaces of the document; around the edges, the two film sheets may bond directly to each other.
A laminated assembly of this kind provides excellent protection for the identification document. The biaxially oriented polyester outer film effectively withstands a great deal of abuse. It remains hard, tough, and abrasion-resistant with little change due to aging; the transparency of the film is also little changed with age. The protective film makes it difficult to alter the identification card for purposes of fraud or forgery, although alteration can sometimes be effected by skillful, careful work.
Although highly effective and useful, identification documents protected by laminated covers of biaxially oriented polyester film have not been suitable for a number of applications. Thus, the biaxially oriented polyester film on the outer surface of a document assembly of this kind cannot be effectively embossed after lamination; indeed, it is extremely difficult to emboss at any time because the heat, pressure, and time requirements for effective embossure are excessive. Furthermore, it is difficult to obtain effective adherence between any supplementary external film and the surface of the hard polyester film. For example, in those applications in which it is desirable to provide a magnetizable strip on the protected document for the recording of an identification number or other security information, it becomes necessary to locate the magnetizable strip in the interior of the laminated document assembly. An inside location for a magnetizable strip is not desirable because the protective laminate increases the spacing between the strip and any recording or reading transducer. Moreover, with a protected document assembly of this construction, the document cannot be signed or otherwise validated by the user after lamination has been completed because the biaxially oriented base film on the outer surface of the document assembly does not accept ordinary inks; the ink wipes off.